Bubble-free, high barrier vinylidene chloride polymer films and process of preparation

Abstract

This invention is directed to improved bubble-free, high barrier film materials prepared from substantially plasticizer-free vinylidene chloride polymer compositions containing small amounts of magnesium oxide; and to a process for the preparation of such improved films.

What is claimed is: 
     
       1. An improved process for preparing extruded vinylidene chloride polymer film containing modifying amounts of an ethylene-vinyl acetate copolymer, said film being substantially free from bubbles, holes and white specks which process comprises a. preparing a blend of (a) a dry, powdered, nonplasticized normally crystalline vinylidene chloride polymer containing from about 70 to about 95 percent by weight of vinylidene chloride interpolymerized with from about 30 to about 5 percent by weight of at least one monoethylenically unsaturated monomer copolymerizable with vinylidene chloride, with (b) from about 0.05 to about 1 percent based on polymer weight of magnesium oxide having an average particle size of less than about 0.5 micron and wherein said blend is prepared by introducing said magnesium oxide beneath the surface of the mass of dry vinylidene chloride polymer particles .[.while said particles are maintained in motion.]. and where said magnesium oxide coats said particles prior to contact of said magnesium oxide with a metal surface.   2. removing from said blend any agglomerate having a diameter in excess of about 500 microns, then   3. admixing said blend with said ethylene-vinyl acetate copolymer in an extruder which is used to thermally fabricate the admixture into film form.   
     
     
       2. The process of claim 1 wherein said normally crystalline vinylidene chloride polymer is a copolymer of vinylidene chloride and vinyl chloride. 
     
     
       3. The process of claim 2 wherein said polymer is a copolymer of about 85 percent by weight vinylidene chloride and 15 percent by weight vinyl chloride.